1. Field of the Invention
The present invention relates to an ink jet printing apparatus and an ink jet printing method in which printing is performed using an ink jet ejection section capable of ejecting an ink based on print data and a process liquid ejection section capable of ejecting a process liquid serving to improve the printability of the ink.
2. Description of the Related Art
A serial scan ink jet printing apparatus prints an image on a print medium by repeating an operation of moving a print head in a main scanning direction, while ejecting an ink from the print head, and an operation of conveying the print medium in a sub-scanning direction crossing the main scanning direction. The print head includes a large number of nozzles formed therein to eject the ink. When the image is printed, the ink is ejected through nozzles corresponding to image data.
Japanese Patent Laid-Open No. H11-309882 (1999) describes a printing apparatus in which a print head ejects not only an ink but also a process liquid so that the process liquid serves to improve the printability of the ink. The printing apparatus is configured to thin out (cull) locations on a print medium to which the process liquid is to be applied when the printing density of the ink has at least a predetermined value, in order to avoid applying more process liquid than required to prevent an increase in running costs and image degradation associated with cockling or beading.
In the ink jet printing apparatus, the ejection amount of the ink or process liquid is likely to vary depending on the temperature of the print head. A variation in ejection amount may lead to degradation of image quality (a variation in density or an uneven density). In particular, if the number of ink ejections (the number of ink dots formed) per unit print area on the print medium is large, the temperature of the print head is likely to rise to increase the ejection amounts of the ink and the process liquid. Thus, the image quality is likely to be degraded. Furthermore, in the serial scan printing apparatus, if a print range per scan is large and if the print head has a high scan speed, the temperature of the print rises sharply during the scan. Thus, similarly, the image quality is likely to be degraded.